Coastal Ocean Modeling

... To appear in: Ocean and Coastal Management Received Date: 6 September 2010 Revised Date: 25 May 2011 Accepted Date: 10 June 2011 Please cite this article as: Marchand M, Sanchez-Arcilla A, Ferreira M, Gault J, Jimenez J, Markovic ... Ivana 11, HR-21000 Split, Croatia. ...

This study seeks to better understand the impact of seasonal river input on the Bay of Bengal (BoB) using the Regional Ocean Modeling System (ROMS). To quantify the effects, two parallel climatological simulations (with and without rivers) were carried out for fifteen years. While the temperatures at river mouths along the model’s coastal boundary were relaxed to the monthly climatology, observation-based reconstructed seasonal cycles were provided for salinity with monthly discharges for ten selected rivers. The result shows significant improvement (50–70%) in the model-simulated near-surface salinity, freshwater plume, stratification, mixed-layer depth and barrier-layer thickness (BLT) with river input. The river input reduced the domain-averaged annual surface salinity and surface density by 0.99 psu and 0.73 kg/m3, respectively, when compared to the no-river simulation.

One of the major impacts of river inclusion in the simulation is the formation, dispersion and demise of the freshwater plume system in the Bay. Two separate large-scale (Kelvin Number≫1) freshwater plumes form by surface-advection during April–May, one near the Ganges–Brahmaputra–Meghna (GBM) river system mouths at the head of the Bay, and another further south near the mouths of the Irrawaddy–Sittang–Salween (ISS). They merge and evolve as one plume system to cover almost half of the domain in October and to occupy the largest volume in November. The formation and dispersion of the plume system correspond well with freshening in the northern Bay, affecting seasonal stratification with the formation of barrier layer, and subsequent advection of the freshwater by eddies and fronts along the East India Coastal Current (EICC). The simulated domain-averaged BLT was minimum during March–May and maximum during October–February. Simulations indicate that the river input is necessary in addition to precipitation-minus-evaporation in setting up the near-surface stratification and for the formation of barrier layer in the BoB.

Numerical modelling has become an essential component of today's coastal planning, decision support and risk assessment. High-resolution modelling offers an extensive range of capabilities regarding simulated conditions, works and practices and provides with a wide array of data regarding nearshore wave dynamics and hydrodynamics. In the present work, the open-source TELEMAC suite and the commercial software MIKE21 are applied to selected coastal areas of South Italy. Applications follow a scenario-based approach in order to study representative wave conditions in the coastal field; the models' results are intercompared in order to test both their performance and capabilities and are further evaluated on the basis of their operational use for coastal planning and design. A multiparametric approach for the rapid assessment of wave conditions in coastal areas is also presented and implemented in areas of the same region. The overall approach is deemed to provide useful insights on the tested models and the use of numerical models – in general – in the above context, especially considering that the design of harbours, coastal protection works and management practices in the coastal zone is based on scenario-based approaches as well.

Among the upwelling processes at the brazilian coast, probably the most well known and well studied is the Cabo Frio upwelling system. Occurring at spring and summer, this process has been shown to be stronger during summer seasons and more
frequent at spring seasons. During these seasons, the presence of a strong northeast wind acting at the Cabo Frio region causes the outcropping of the SACW, due the Ekman dynamic. The presence of the SACW at the coastal zone may cause a gradient
of 10 ◦ C of temperature comparing to the offshore water. Besides the wind action, the Cabo Frio region presents some features that contributes to the upwelling event, such
as the small extension of the continental shelf, the abrupt change in coastline direction and the interaction between the upwelling and the meso-scale system, such as the Bra-
zil Current meanders. Although well studied in its path through the coast of Rio de Janeiro, only a few works have investigated the upwelling plume around the Cabo Frio Island and around the city of Arraial do Cabo. Because of this lack of information, the current work pretends to investigate the distribution and formation of the upwelling in this region. The ROMS model was chosen to simulate the dynamics of the upwelling plume. In this work is used the technique of nesting two grids, where a small resolution simulation is used to feed the high resolution simulation. Three experiments were conducted, being one with only the tide as a forcing, another one with only the wind
and the third one, with both forcings acting. The results has shown that the wind is the most important component in the area and that in the bottom the SACW enters in the Cabo Frio Island bay through the north channel and in the south channel the cold water gets constrained by the bathymetry. The SACW could also be seen around the Cabo Frio Island, outside the bay. At the surface, the wind action prevented the entrance of the upwelled SACW in the island bay and followed its path to the south.